/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.dubbo.config.utils;

import org.apache.dubbo.common.utils.StringUtils;
import org.apache.dubbo.config.ReferenceConfig;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * A simple util class for cache {@link ReferenceConfig}.
 * <p>
 * {@link ReferenceConfig} is a heavy Object, it's necessary to cache these object for the framework
 * which create {@link ReferenceConfig} frequently.
 * <p>
 * You can implement and use your own {@link ReferenceConfig} cache if you need use complicate
 * strategy.
 */
public class ReferenceConfigCache {

  public static final String DEFAULT_NAME = "_DEFAULT_";
  /**
   * Create the key with the <b>Group</b>, <b>Interface</b> and <b>version</b> attribute of {@link
   * ReferenceConfig}.
   * <p>
   * key example: <code>group1/org.apache.dubbo.foo.FooService:1.0.0</code>.
   */
  public static final KeyGenerator DEFAULT_KEY_GENERATOR = referenceConfig -> {
    String iName = referenceConfig.getInterface();
    if (StringUtils.isBlank(iName)) {
      Class<?> clazz = referenceConfig.getInterfaceClass();
      iName = clazz.getName();
    }
    if (StringUtils.isBlank(iName)) {
      throw new IllegalArgumentException("No interface info in ReferenceConfig" + referenceConfig);
    }

    StringBuilder ret = new StringBuilder();
    if (!StringUtils.isBlank(referenceConfig.getGroup())) {
      ret.append(referenceConfig.getGroup()).append("/");
    }
    ret.append(iName);
    if (!StringUtils.isBlank(referenceConfig.getVersion())) {
      ret.append(":").append(referenceConfig.getVersion());
    }
    return ret.toString();
  };
  static final ConcurrentMap<String, ReferenceConfigCache> cacheHolder = new ConcurrentHashMap<String, ReferenceConfigCache>();
  private final String name;
  private final KeyGenerator generator;
  ConcurrentMap<String, ReferenceConfig<?>> cache = new ConcurrentHashMap<String, ReferenceConfig<?>>();

  private ReferenceConfigCache(String name, KeyGenerator generator) {
    this.name = name;
    this.generator = generator;
  }

  /**
   * Get the cache use default name and {@link #DEFAULT_KEY_GENERATOR} to generate cache key. Create
   * cache if not existed yet.
   */
  public static ReferenceConfigCache getCache() {
    return getCache(DEFAULT_NAME);
  }

  /**
   * Get the cache use specified name and {@link KeyGenerator}. Create cache if not existed yet.
   */
  public static ReferenceConfigCache getCache(String name) {
    return getCache(name, DEFAULT_KEY_GENERATOR);
  }

  /**
   * Get the cache use specified {@link KeyGenerator}. Create cache if not existed yet.
   */
  public static ReferenceConfigCache getCache(String name, KeyGenerator keyGenerator) {
    ReferenceConfigCache cache = cacheHolder.get(name);
    if (cache != null) {
      return cache;
    }
    cacheHolder.putIfAbsent(name, new ReferenceConfigCache(name, keyGenerator));
    return cacheHolder.get(name);
  }

  @SuppressWarnings("unchecked")
  public <T> T get(ReferenceConfig<T> referenceConfig) {
    String key = generator.generateKey(referenceConfig);

    ReferenceConfig<?> config = cache.get(key);
    if (config != null) {
      return (T) config.get();
    }

    cache.putIfAbsent(key, referenceConfig);
    config = cache.get(key);
    return (T) config.get();
  }

  /**
   * Fetch cache with the specified key. The key is decided by KeyGenerator passed-in. If the
   * default KeyGenerator is used, then the key is in the format of <code>group/interfaceClass:version</code>
   *
   * @param key cache key
   * @param type object class
   * @param <T> object type
   * @return object from the cached ReferenceConfig
   * @see KeyGenerator#generateKey(ReferenceConfig)
   */
  @SuppressWarnings("unchecked")
  public <T> T get(String key, Class<T> type) {
    ReferenceConfig<?> config = cache.get(key);
    return (config != null) ? (T) config.get() : null;
  }

  void destroyKey(String key) {
    ReferenceConfig<?> config = cache.remove(key);
    if (config == null) {
      return;
    }
    config.destroy();
  }

  /**
   * clear and destroy one {@link ReferenceConfig} in the cache.
   *
   * @param referenceConfig use for create key.
   */
  public <T> void destroy(ReferenceConfig<T> referenceConfig) {
    String key = generator.generateKey(referenceConfig);
    destroyKey(key);
  }

  /**
   * clear and destroy all {@link ReferenceConfig} in the cache.
   */
  public void destroyAll() {
    Set<String> set = new HashSet<String>(cache.keySet());
    for (String key : set) {
      destroyKey(key);
    }
  }

  @Override
  public String toString() {
    return "ReferenceConfigCache(name: " + name
        + ")";
  }

  public static interface KeyGenerator {

    String generateKey(ReferenceConfig<?> referenceConfig);
  }
}
